The present invention relates to a fluidic variable focal length optical lens and a method for manufacturing the same.
There is an ever-increasing need for miniaturization and cost-effective solutions for lenses as part of imaging systems with either static or dynamic functions. In conventional optical imaging systems and cameras with auto-focus and zooming options, the physical positioning of a movable lens element to focus an image onto an image sensor or to change the overall magnification of the system is often realized by a manual operation of a bulky mechanical positioning system based on a complex arrangement of gears. The large physical dimension of a focusing and zooming system makes it difficult to place such optical zooming functions onto cell phone cameras or, if this is done nevertheless, the image quality is low compared to that of conventional photo cameras. Moreover, mechanical positioning systems are subjected to corrosion or mechanical wearing processes such as abrasion.
In order to improve the functionalities, increase the efficiency and decrease the costs of a zoom objective, an auto-focus option or other (adjustable) optical element for miniature imaging systems, alternative solutions have been adopted, including lenses of continuously varying focal length.
In the art, known design of variable lenses employed for optical imaging and adaptive optics make use of various fundamental processes for varying the focal length, wherein the basic idea is to either change the geometry or the optical properties of the lens material. Known designs of variable lenses use, for instance, processes such as a deformation of an elastic membrane as provoked by an externally exerted hydraulic pressure on the surrounding medium, the variation of contact angle respectively meniscus of a two-fluid-interface forming a lens by means of electro-wetting effect, volume variation of lens materials via thermal contraction respectively dilation or pH variation in organic gels' lenses, refractive index variation in lenses made of liquid crystals by electrically changing the liquid crystals' orientation, lenses made of electro-optic materials whose bulk polarization can be changed by varying an applied electric field, and lenses made of thermo-optic materials which respond to temperature variation.
In WO 2007/069213 A2, U.S. Pat. No. 6,188,526 B1, J. Draheim et al., “Fabrication of a fluidic membrane lens system”, J. Micromech. Microeng. 19 (2009) 095013 and U.S. Pat. No. 7,580,195 B2, several different focus fluid lens devices having a fluidic chamber are described, wherein a membrane is deformed by an activation of some actuator configured to act as a pump so as to change a focal length of the respective lens device. In WO 2007/069213 A2, the actuator has two distinct states of deformation only, which essentially result in two different focal lengths as well. In U.S. Pat. No. 6,188,526 B1, a pump zone and a lens zone of the fluidic chamber laterally overlap each other, so that the construction is complicated. A disadvantage of the lens device as described in J. Draheim et al., “Fabrication of a fluidic membrane lens system”, J. Micromech. Microeng. 19 (2009) 095013 is that it uses channels and, therefore, is characterized by a relative complex structure. In U.S. Pat. No. 7,580,195 B2, the structure of the lens device has one fluidic chamber filled with a fluidic medium with the membrane separating the fluidic medium from the environmental medium, so that the control of the focal length is difficult due to dependencies on environmental physical conditions.
However, a general problem of known designs is that they present restrictions regarding the degree of miniaturization, compactness and robustness.